In recent years, in advance of suppression of emission of harmful air pollutants, mercury in an exhaust gas is a substance of a greatest concern. In particular, in movement of enshrining PRTR (Pollutant Release and Transfer Register) into law, it can be considered that monitoring heavy metals emitted from a waste incineration facility and the like will become an important problem in the future, and interests in mercury in an exhaust gas are increasing. Since mercury in a gas such as an exhaust gas containing various kinds of reactive substances changes its chemical conformation and its behavior greatly varies, it is considered that measurement in accordance with each conformation is necessary in regard to clarification of actual conditions and an extraction ratio. Further, in order to comprehend fluctuations in a short time and comprehend specification of a material concerning chemical reaction with the mercury or the influence by a combustion condition, analysis in accordance with each chemical conformation of the mercury must be rapidly carried out.
On the other hand, as a conventional method of measuring mercury in an exhaust gas, a method for measuring all of mercury by using a potassium permanganate solution specified by Japan Industrial Standards (JIS K-0222), a method for measuring metal mercury by using gold amalgam, and others are standard.
Furthermore, there is proposed in Japanese utility model publication No. 19250/1983 a technique of fractionating and measuring molecular mercury consisting of a mercury compound and metal mercury consisting of mercury atoms when such both types of mercury exist in a gas. As shown in FIG. 3, according to this technique, a molecular mercury capturing portion 101 obtained by filling powder of a heat-resisting porous material such as diatomaceous earth in a quartz tube including an electric wire heater 102 on an outer side thereof and a metal mercury capturing portion 107 obtained by filling in a quartz tube including an electric wire heater 108 on an outer side thereof a material obtained by coating the surface of powder of a heat-resisting porous material such as diatomaceous earth with gold are arranged in series, a spectral line absorption cell 110 and an exhaust tube 117 are connected to an outlet of the metal mercury capturing portion 107 through a three-way change-over valve 109, and they are connected to a pump 112 through a filter 111. Moreover, the pump 112 is connected to a flow meter 116 through a branch tube including needle valves 113 and 114 and a three-way change-over valve, an exhaust flow quantity is measured, and then a gas is exhausted.
According to this apparatus, a gas 100 containing mercury led from a sample intake tube 104 by operating the three-way change-over valve 103 is passed through the molecular mercury capturing portion 101 and the metal mercury capturing portion 107, and then exhausted through the pump 112, the branch tube having the needle valve 113 and the flow meter 116 from the exhaust tube 117 without passing through the cell 110. Then, the molecular mercury is absorbed into and captured by the porous material of the molecular mercury capturing portion 101, and the metal mercury which is hardly absorbed by the porous material is captured by forming the amalgam between the metal mercury and gold surface of the porous material. Thereafter, air purified by a filter 106 and a dehumidifier 105 is passed through the molecular mercury capturing portion 101, the metal mercury capturing portion 107 and others and the remaining sample gas is exhausted by switching the three-way change-over valve 103 and connecting the branch tube including the needle valve 114 to the flow meter 116. After scavenging, the amalgam is decomposed by heating the metal mercury capturing portion 107 to approximately 600° C., the metal mercury is disengaged to be led to the cell 110 together with a carrier gas, and the metal mercury is detected by atomic absorption analysis. Subsequently, the molecular mercury in a compound absorbed in the porous material is disengaged by heating the molecular mercury capturing portion 101 to approximately 600° C., it is supplied to the metal mercury capturing portion 107 together with the carrier gas, it is completely decomposed in the metal mercury capturing portion 107 to be turned into metal mercury, and then it is led into the cell 110, thereby detecting the metal mercury by atomic absorption analysis. In this manner, the molecular mercury and the metal mercury can be separately measured.
In addition, in recent years, analysis based on each chemical conformation is attempted also in the United States. This analysis based on each chemical conformation is batch processing carried out by causing the water-soluble mercury to be absorbed by potassium chloride in the former stage, causing the metal mercury to be absorbed by a potassium permanganate solution in the latter stage and measuring a quantity of mercury contained in each solution.
Additionally, an analysis method using a potassium permanganate solution which is specified by Japan Industrial Standards is a batch processing technique, and its target is restricted to monitoring a concentration of all of mercury including all conformations. Therefore, it is impossible to obtain a result of continuous analysis based on each chemical conformation, e.g., fractionation and analysis of the water-soluble mercury and the metal mercury. Further, since the measuring method using gold amalgam aims at only the metal mercury, a result of continuous analysis based on each chemical conformation can not be obtained.
Furthermore, since the fractional detection apparatus for the molecular mercury and the metal mercury disclosed in Japanese utility model publication No. 19250/1983 corresponds to batch processing by which the molecular mercury and the metal mercury are captured by causing them to be absorbed into the porous material or forming the amalgam, scavenging is carried out, the metal mercury capturing portion 107 is first heated to approximately 600° C. and the molecular mercury is disengaged and measured and the molecular mercury capturing portion 101 is then heated to approximately 600° C. to disengage and measure the molecular mercury, sampling is time-consuming, and time is also required for processing before and after sampling, heating carried out for two times and sample analysis. Also, rapid analysis based on each chemical conformation is hardly carried out, and there is a problem of requiring a large amount of cost.
Therefore, it is difficult to comprehend fluctuations in mercury contained in a waste combustion exhaust gas in a short time by any analysis method.
Thus, it is an object of the present invention to provide a method and an apparatus for continuously fractionating and analyzing metal mercury and water-soluble mercury, which continuously separate and measure the mercury in an exhaust gas in accordance with each chemical conformation to display the result in real time.